The invention relates to a method for checking the state of the gas fill in the insulating cavity of an insulating glass pane, and to an insulating glass pane, comprising at least two glass plates which are spaced apart from one another, and an edge joining strip which surrounds and joins together the glass plates in the region of their edges, in which the edge joining strip seals and delimits an insulating cavity which is located between the glass plates, and in which the insulating cavity is filled with a fill gas which is not air.
Insulating glass panes of this nature are generally known. They obtain for example a thermal insulating action by means of the gas fill in the insulating cavity, which is filled with a gas with a poor thermal conductivity and is sealed with respect to the outside by means of the edge joining strip. The fill gas used is often inert gases or other gases or gas mixtures which have a very low thermal conductivity. However, during the service life of an insulating glass pane, the sealing effect of the edge joining strip may deteriorate owing to aging of the sealing means used therein, so that gas is exchanged between the insulating cavity of the insulating glass pane and the surrounding atmosphere. In this event, air gradually enters the insulating cavity, so that the insulating action of the insulating glass pane decreases owing to the thermal conductivity of air, which is better than that of the fill gas.
DE 31 05 740 C2 has disclosed a method for checking the fill gas in insulating glass panes, in which method the passage time of a heat pulse in the fill gas is measured. For this purpose, a small heater plate is provided on a glass plate, and a current pulse is applied, generating a temperature rise on the surface of the heating plate, and a receiver, which detects the temperature rise generated on the heating plate, is provided on the other glass plate. With a given distance between the heating plate and the receiver, the passage time of the temperature pulse between the transmitter and the receiver represents a measure of the insulating action. This known measurement of the insulating action requires a high level of outlay on equipment and can only be carried out as a quality assurance test during production or in the course of special functional checks. It cannot be used to continuously monitor the functioning of the insulating glass pane.
Another method for checking the fill gas in insulating glass panes is known from DE 34 39 216 C1, in which the two adjacent glass plates are subjected to low-frequency mechanical vibrations, while characteristic vibration properties, such as the resonance frequency or direction value, are determined, and these properties again constitute a measure of the insulating action of the insulating glass pane. This method also involves a high level of outlay on equipment and is not suitable for continuous functional testing.
A further method for checking the fill gas in insulating glass panes is known from DE 34 39 405 C2, in which a sound signal is applied to a glass plate, and the propagation velocity of the sound in the pane cavity is determined using a receiver provided on the other glass plate; the composition of the fill gas and therefore of the insulating action can be calculated from the sound propagation velocity. The outlay on equipment which is required means that this method is also unsuitable for continuous monitoring of the insulating action of an insulating glass pane.
It is an object of the present invention to provide a method and a device which make it possible to monitor the insulating action of an insulating glass pane essentially continuously through the service life of the insulating glass pane and to detect significant deterioration in the insulating action.
That part of the invention which relates to the method is achieved by the fact that a sensor means, which is provided in the insulating cavity of the insulating glass pane, is exposed to the atmosphere in the insulating cavity, and that the sensor means reacts to a change in the composition of the fill gas by giving a signal. Integrating the sensor means in the assembly of the insulating glass pane provides a simple monitoring feature which is inexpensive and does not require a particularly high outlay on equipment.
The sensor means preferably reacts by visibly changing color. The constant visibility of the sensor means in the interior of the insulating glass pane, in conjunction with the change in color, makes it easy to establish a defect in the insulating glass pane.
In a particularly preferred embodiment, the sensor means reacts to a constituent of air, such as oxygen or nitrogen, preferably when this constituent exceeds a threshold value.
Consequently, if, during the service life of the insulating glass pane, gas is exchanged between the insulating cavity and the outside atmosphere, the composition of the fill gas or of the fill gas mixture changes, and this is indicated by the signal given by the sensor means. The sensor means can either react to a constituent of the fill gas falling below a threshold or to a constituent of air exceeding a threshold.
In a particularly preferred embodiment, the sensor means reacts to the presence of oxygen above a threshold concentration, in which event the change in color can be seen from the outside and serves to indicate a deterioration in the insulating action of the insulating glass pane.
Another part of the invention is to provide a sensor in the insulating cavity, which sensor reacts and gives a signal if the composition of the fill gas changes.
Preferably, the sensor has a constituent which undergoes a visible change in color in the composition if the fill gas changes.
In this case, that constituent of the sensor which changes color preferably reacts by changing color in the presence of a constituent of air, such as oxygen or nitrogen.
The change in color preferably only takes place in the event of a predeterminable threshold concentration of oxygen or nitrogen being exceeded.
It is particularly advantageous if the sensor is arranged on the inside, facing toward the insulating cavity, of at least one of the glass plates, thus improving the visibility of the sensor.
The sensor is preferably formed by a sensor layer which extends at least along part of the edge of the glass plate, preferably along the entire periphery in the edge region of the glass plate. This sensor layer may be applied to the glass plate by screen printing, for example. If the sensor layer extends along the entire periphery in the edge region of the glass plate, it is possible to determine the site of a leak in the edge region of the insulating glass pane at an early stage, since the sensor layer will change color more quickly in the area of the leak, due to the intensified exchange of gas which takes place in this area.
If the composition of the fill gas or of the fill gas mixture changes, the sensor may also emit an electric signal which can be received by a stationary or mobile evaluation and display unit outside the insulating glass pane. This configuration allows both remote monitoring in a building with a large number of insulating glass panes and monitoring of the insulating action by means of a display unit which is or can be arranged outside the pane. An electric signal which is generated in this way may moreover be assessed as an alarm signal in the event of one of the glass plates being broken if, in such a case, a particularly abrupt change in the composition of the gas is detected.